1. Field of the Invention
The present invention relates to a brushless DC motor to the structure of the stator of a brushless DC motor, the stator including a magnetic conductive tube and a pole plate.
2. Description of the Related Art
Referring to FIG. 1, a conventional brushless DC motor and stator comprises a metal tube 91 with outer surface surrounded by a coil 92, an upper pole plate 93, a lower pole plate 94 and a circuit board 95. The upper plate 93 and the lower plate 94 are formed by a plurality of stacked silicon steel plates so as to increase the area adjacent to the permanent magnet of the rotor. Because it consists of a plurality of silicon steel plates the conventional motor and stator are complex, the cost of manufacture is high, and much more of the material.
Furthermore, one end of the metal tube 91 has an annular flange 911 which is larger than the diameter of the tube. When the other end of metal tube91 being fixed, the annular flange 911 limits the coil 92, the upper plate 93, the lower plate 94 and the circuit board 95, and thus the thickness of annular flange 911 increases the thickness of the stator. In order to decrease the thickness of the stator, the annular flange 911 may be removed for the best design.
Furthermore, U.S. Pat. No. 4,891,567, issued on Jan. 2, 1990 to Fujitani et al., discloses a pole plate having a pole which is bent in a right angle to the pole plate. The poles are bent toward each other, so that the poles cover the outer peripheral space of the coil seat. Thus, the pole plates are pressed and combined on the stator, after coils have been wounded on the coil seat of the stator. However, the poles of the stator are arranged to face each other because the coils must first be wounded on the coil seat of the stator, and then the pole plates pressed on the bobbin to form the stator. The pressing process of pole plates into a bobbin with a wound has the disadvantage that the coil wire may be cut or cut broken, the bobbin pressed, and the enameled layer of wires damaged. Wires of the coil suffer from starting current pulses in the long term resulting in the degrading of the coil assembly and resulting in deterioration of rotation of the motor and shortening motor life.